/**
 * qccr.com Inc.
 * Copyright (c) 2018-2020 All Rights Reserved.
 */
public class _06局部最小值 {

        // arr 相邻的数不相等！
        public static int oneMinIndex(int[] arr) {
            if (arr == null || arr.length == 0) {
                return -1;
            }
            int N = arr.length;
            if (N == 1) {
                return 0;
            }
            if (arr[0] < arr[1]) {
                return 0;
            }
            if (arr[N - 1] < arr[N - 2]) {
                return N - 1;
            }
            int L = 0;
            int R = N - 1;
            // L...R 肯定有局部最小
            while (L < R - 1) {
                int mid = (L + R) / 2;
                if (arr[mid] < arr[mid - 1] && arr[mid] < arr[mid + 1]) {
                    return mid;
                } else {
                    if (arr[mid] > arr[mid - 1]) {
                        R = mid - 1;
                    } else {
                        L = mid + 1;
                    }
                }
            }
            return arr[L] < arr[R] ? L : R;
        }

        // 生成随机数组，且相邻数不相等
        public static int[] randomArray(int maxLen, int maxValue) {
            int len = (int) (Math.random() * maxLen);
            int[] arr = new int[len];
            if (len > 0) {
                arr[0] = (int) (Math.random() * maxValue);
                for (int i = 1; i < len; i++) {
                    do {
                        arr[i] = (int) (Math.random() * maxValue);
                    } while (arr[i] == arr[i - 1]);
                }
            }
            return arr;
        }

        // 也用于测试
        public static boolean check(int[] arr, int minIndex) {
            if (arr.length == 0) {
                return minIndex == -1;
            }
            int left = minIndex - 1;
            int right = minIndex + 1;
            boolean leftBigger = left >= 0 ? arr[left] > arr[minIndex] : true;
            boolean rightBigger = right < arr.length ? arr[right] > arr[minIndex] : true;
            return leftBigger && rightBigger;
        }

        public static void printArray(int[] arr) {
            for (int num : arr) {
                System.out.print(num + " ");
            }
            System.out.println();
        }

        public static void main(String[] args) {
            int maxLen = 100;
            int maxValue = 200;
            int testTime = 1000000;
            System.out.println("测试开始");
            for (int i = 0; i < testTime; i++) {
                int[] arr = randomArray(maxLen, maxValue);
                int ans = oneMinIndex(arr);
                if (!check(arr, ans)) {
                    printArray(arr);
                    System.out.println(ans);
                    break;
                }
            }
            System.out.println("测试结束");

        }
}
